The objective of this research program is to solve selected key technical problems in radiation therapy that limit the effectiveness of present treatment. The proposed research program consists of the following interdependent research projects. Projects proposed in Treatment Planning are: Measurements of Anatomical Inhomogeneities, and Human-Engineered Minicomputer System for Improved Display and Three-Dimensional Treatment Planning in Radiation Therapy. Projects proposed in Treatment Delivery are: Dose Optimization by Computer Controlled Radiation Treatment; Elctromechanical Components, System Dynamics, and Control Strategies for an Automated Radiation Therapy System; Radiation Therapy Field Scanner/Imaging System; Photon Beam Flattening Filters; and High Resolution Dose Measurements with Stimulated Phosphorescence. Projects proposed in Evaluation of Computer Controlled Radiation Therapy and Associated Topics are: Clinical Trials of Optimized Dose Distributions; Dose Optimization with Non-Computerized Isocentric Machines; Evaluation of Treatment Plans; and Decision Analysis in Cancer Diagnosis and Therapy. The problems selected satisfy the criterion that the successful outcome of each project will contribute to an advance in the quality of routine radiation therapy and, as part of the overall program, will also lead to new and improved capabilities in optimizing dose to the tumor while minimizing exposure to healthy tissues.